1. Field of the Invention
The invention lies in the area of electrical circuits. More specifically, the invention discloses a voltage regulator circuit for a solar powered battery charging device. More exactly, the invention is an electrical circuit that cuts off power from a photovoltaic panel (PVP) to a battery being charged that prevents discharge of the battery through the PVP at night time, and that reinitiates battery charging the following day.
2. Description of the Prior Art
A previous method dealing with the problem of keeping a battery charged by PVP means, and not overcharging the battery in such manner that might do damage, yet preventing discharge of the battery through the PVP once the sun has set, involved use of a simple diode component situated between the PVP and the battery to be charged along with a PVP matched in size and voltage to that of the battery being charged. The diode passes current one way to the battery during the daylight charging hours and is reverse biased at night thereby preventing battery current from returning from the battery back through the PVP when the electromotive force (EMF) in the battery exceeds that of the PVP. The simple diode procedure, however, is limited to very elementary battery charging situations, and will not prevent overcharging of the batteries unless the PVP is exactly balanced to generate just that amount of electrical energy from solar energy that is used on a daily basis by the standby battery being charged.
Other more elaborate, sophisticated, and expensive devices that have been designed have used battery temperature/pressure compensation feedback means to sense the voltage level of charge in a battery during the charging process to regulate the uncontrolled PVP charging of the battery.
In addition, elaborate voltage level timing devices have been designed that use timing and battery voltage sampling intervals. In essence, these solid state devices periodically disconnect the PVP array, allow a battery voltage settling time interval for EMF battery chemical stabilization, at the end of which the battery voltage level is checked and finally reconnected to the PVP battery charger if the desired voltage is not yet obtained.
Another application dealt with a simplified voltage regulator circuit that permitted varying light intensity PVP recharging of secondary batteries. The regulator circuit electronically shunted serially connected regions of a PVP to avoid overcharging during periods of high light intensity or full battery charge conditions. The regulator circuitry provided minimal series resistance to the PVP and required nominal driving power; however, this application again is limited to relatively low current and low voltage applications.
Another prior application dealt with a dual parallel circuit extending from a PVP in which a first current limiting diode was positioned within one of said parallel circuits, and the battery to be charged was positioned within the second parallel circuit in series with a second diode. The terminals of the components of the circuit were connected such that current from the PVP was limited by the first diode means so as to prevent overcharge of the secondary battery, while the second diode means was connected so as to prevent reverse current flow through the PVP when the voltage of the secondary battery was higher than that of the PVP, i.e. when the sun sets. Again, this application is limited to low current voltage applications, and the PVP necessarily must be equally balanced with the needs of the battery to be charged.
In summary, most of the prior art devices were predominantly solid state devices, substantially more elaborate and costly than applicant's invention, and required that the PVP be matched in size with the battery being charged. As such, there exists a continuing need for a more reliable, less expensive means for controlling the charge procedure utilizing a PVP of unspecified size to charge various batteries in remote stand-by situations. The invention is substantially less expensive than other equivalent devices, it uses natural (solar) timing for charge cycles, is highly reliable, i.e. few components indicate inherent reliability, and the PVP size is independent of battery size. The invention's only limitations of any import are that it is limited to one charge cycle per day, and voltage control may vary somewhat in accuracy with respect to temperature variations.